Radio frequency (RF) GaN/AlGaN high electron mobility transistors (HEMTs) typically have a through substrate via (TSV) plug connection for connecting the source at the front-side of the device to a metallization disposed on the back-side of the device. A source plug connection is needed to realize high efficiency, high frequency power applications, and for ease of device packaging. Usually semi-insulating or high-resistivity substrates are required, in order to minimize high frequency losses.
Conventional approaches for realizing a source plug connection, when using semi-insulating or high-resistivity substrates, is a TSV source plug connection. The TSV plug connection is fabricated by forming an opening through the substrate from the substrate back-side after the substrate is thinned, i.e. at the end of the HEMT device fabrication process, and filling the opening with a conductive material. Other conventional front-side source plug connections are fabricated using deep-RIE (reactive ion etching) or laser drilling to form an opening through the substrate from the front-side during frontend processing, through the thick substrate prior to thinning. In each case, the processes involved increase cost and are not fully compatible with standard CMOS (complementary metal oxide semiconductor) processing.